For nearly any major disaster—natural, economic, or military—there was a moment when tragedy could have been prevented.

In just the last decade, experts warned that a subprime mortgage bubble could lead to financial collapse and that a hurricane could devastate New Orleans. But our leaders failed to head off disaster, and the public knew little until it was too late.

Now we face the largest potential Katrina the world has ever seen, an imminent catastrophe we refer to blandly as “climate change.” Neither your mayor, nor your senator, nor certainly, your president has declared a climate emergency. But in the time since you may have watched An Inconvenient Truth, global emissions have worsened, and the scientific predictions have become much more frightening.

The carbon dioxide that we have already put into the atmosphere makes it a near certainty that our oceans will become steadily more acidic, eventually destroying coral reefs and sea life. Glaciers will continue to melt year by year, eventually threatening the water supply of as much as 25 percent of the human population [1]. Sea levels are already rising, and will continue to rise for hundreds of years.

In many parts of the world, the climate emergency has already arrived. An estimated 26 million people have already been displaced by the increases in hurricanes, floods, desertification, and drought brought on by climate change [2]. In the North Atlantic, Category 5 hurricanes, the most destructive kind, occur three to four times more often than they did a decade ago [3].

While no single weather event can be tied directly to global warming, droughts, dust storms, and wildfires are becoming more common worldwide, and climate models predict that trend will accelerate. Southern California’s worst wildfire in 30 years scorched 20,000 acres last spring [1]. And in September, Sydney, Australia, choked on its own version of the Dust Bowl: More than 5,000 tons of orange dirt swirled around the city during one of the region’s worst droughts.

We’re no longer talking about future generations; it’s about us.

Why haven’t our leaders responded? They have been relying on old, conservative estimates of global warming effects. The 2007 Intergovernmental Panel on Climate Change (IPCC) projections used baseline scenarios from the 1990s, when scientists and government leaders assumed that by now, popular and political support would have led us to reduce greenhouse gas emissions [4]. That means politicians and the people they represent have been looking at optimistic projections based on improvements that didn’t happen.

In fact, global fossil-fuel and industrial carbon emissions have grown by 3.5 percent a year since 2000, faster than the worst-case scenario predicted by the Nobel Prize-winning IPCC [4]. Atmospheric carbon dioxide concentrations are now at their highest levels in the last 15 million years, since before humans walked the earth [5].

Lake Mead shrinks, exposing bleached banks. The Mead-Powell system supplies water to Los Angeles, San Diego, and Las Vegas.

U.N. senior official Luc Gnacadja recently told the press that by 2025, 70 percent of the world’s land could be suffering from drought [6]. In the United States, a report by the Union of Concerned Scientists says that in just a couple of decades, average summers in the country’s bread basket, Illinois, could be hotter than the 1988 heat wave that wiped out $40 billion worth of food crops [7]. In the next 12 years, there’s a 50-50 chance that a combination of climate change and overuse will dry up Lakes Mead and Powell, say scientists with the Scripps Institution of Oceanography [8]. Mead and Powell supply 90 percent of Las Vegas’ water, along with irrigation and drinking water for more than 20 million people in Los Angeles and across Nevada and Arizona.

The vast majority of scientists agree that if we keep the Earth’s temperature from rising 3.6 degrees Fahrenheit (2 degrees Celsius) above pre-industrial levels, we have a fighting chance of avoiding the most civilization-shaking impacts of climate change. The G8 leaders agreed to that target at their July meeting.

Shoot past this limit, and the planet’s­ ecosystems may enter a point of no return. We push the Earth into vicious spirals of feedback loops that make things even hotter. Sea ice melts, and the dark, open ocean absorbs more heat. The Amazon rainforest burns and releases even more greenhouse gases into the atmosphere. Weather patterns like El Niño transform from occasional to annual hurricane-brewing phenomena [1]. Grain crops fail [4]. One to 3 billion people face water shortage. The basic systems that support us, our societies, and life on the planet start breaking apart.

We have the wherewithal

We have a choice to make. According to a consensus of hundreds of climate scientists, we can avert crashing the planet only if we make a sharp global U-turn by 2015: Level off emissions worldwide and bring them back down in the next few decades [4].

To do this, we must switch to much more efficient transportation, manufacturing, and buildings, and to solar, wind, tide, and biomass energy. Agriculture must make a rapid switch to organic and ecologically sound practices. The Worldwatch Institute estimates that livestock are responsible for more than half of greenhouse-gas emissions worldwide. We have to stop destroying forests for cattle ranches, palm oil plantations, and paper pulp, so we can preserve their ability to soak up carbon.

We need the world’s governments to form ambitious and binding agreements at Copenhagen and beyond. These agreements need to regulate and put a high price on emissions, and create incentives for a transition to a clean energy economy. The agreements must include help for the Global South in making the transition to a green economy.

We can afford to do this. The Economics of 350, recently released by the Economics for Equity and the Environment Network, says the cost of reducing CO2 to 350 parts per million—the amount necessary to avoid a 3.6-degree temperature rise—would be between 1 percent and 3 percent of world GDP. It will cost far less than the 3.3 percent of GDP spent globally on insurance or the 4 percent-plus of GDP the United States spends on its military. And it will do more than either of those to increase our security.

Investments in renewable energy, building retrofits, and efficient mass transit will put people to work and create whole new industries, kick-starting an economic recovery that immediately benefits ordinary people.

The low-carbon culture we need to prevent climate catastrophe is not a culture of deprivation. We can move away from consumption for consumption’s sake, gaining time to enjoy our lives more fully, and creating a world where our children and grandchildren have the opportunity to thrive.

What’s Holding Us Back?

Contrary to popular perception, the scientific community has reached a broad consensus that global warming is happening and that humans have caused it. So why has the United States been so slow to react to the warnings?

The misinformation sown by industry-­funded climate deniers, the lack of national leadership, and the chronic failure of U.S. media to report the story leave many Americans confused about what to think.

Then there’s the convenient excuse that those of us in developed nations should wait until those in the developing nations, particularly India and China, agree to act at the same speed. That argument ignores the fact that the vast majority of the CO2 currently in the atmosphere came from industrialized nations. U.S. carbon per capita emissions are more than four times China’s and almost 18 times India’s. There’s a fundamental fairness to requiring wealthy nations to clean up the mess we created and to help the poorer ones avoid making the same mistakes. More to the point, the nations of the Global South will only be able to sign on to an agreement that allows them to secure food and an economic future for their citizens. If the deal isn’t fair, it won’t happen.

A Climate Justice Mobilization

The American people effectively mobilized in the buildup to World War II. When we faced a war emergency, we didn’t take half measures: We converted automobile factories to tank factories and learned to recycle everything. The unemployed got jobs—even those previously excluded from the workforce, like women and people of color.

The war mobilization was the organizing principle of life, and many believe it not only got us out of the Great Depression, it also launched us into decades of sustained prosperity. Think about the sense of shared purpose that resulted from that mobilization, and you begin to see the potential.

Today, a 21st-century people’s movement is building, motivated by the climate crisis coupled with the opportunity for a clean-energy future. Youth from rich countries are supporting climate justice for the poor. Scientists like James Hansen are risking arrest along with social justice advocates. Union officials are standing with greens.

Like other social movements that have changed our world, the climate justice movement is getting traction by taking the high ground. It is sticking to strategies that are nonviolent and inviting ordinary people to be part of creating a clean and prosperous world. And it is insisting on a fair shake for all the world’s people.

Economic Change

People are energized by the prospect of a green economy and new, clean technologies, and they want the opportunity not only to avert a climate catastrophe, but to help build a better future. Seventy-seven percent of those polled by Public Agenda say “investing in creating ways to get energy from alternative sources like solar and wind” is the best way to get the economy going, while just 16 percent believe “investing in finding more sources of oil, coal, and natural gas” is the answer.

This excitement is especially evident among those who were left out of the last wave of economic growth and today are sidelined by the so-called “jobless recovery.” Among the supporters of green jobs and clean energy are urban youth, steelworkers, solar developers, architects, farmers, and all sorts of people who see the prospects for a green economic recovery that actually puts people to work.

Workplaces, homes, places of worship, and schools are being upgraded to become more climate-friendly and less costly to operate. Communities are making serious commitments to re­ducing their carbon emissions, restructuring their economies, and making neighborhoods green, resilient, and inclusive (see Towns Rush to Make the Low-Carbon Transition).

Buy-local campaigns are cutting down on long-distance transport and climate emissions. The strengthened local economies offer diverse livelihoods that meet people’s immediate needs while weaving together the relationships that help people weather anything from an economic downturn to climate catastrophe.

We’ll have to ramp up those changes to address the climate crisis in the time and at the scale we have available, and many Americans know that won’t be easy; 48 percent of those polled by Public Agenda say reducing the effects of global warming will require major sacrifices.

No social movement gets everyone on board. But movements succeed when thousands change their attitudes and practices, and then speak out and influence others. A climate-friendly life is becoming “cool,” even heroic.

In the old economy, the heroes were the ones who made lots of money even if it was at the expense of other people or the planet. The new heroes are those who defend the planet. They restore land that is degraded and poisoned, clean up sources of climate-altering pollution, rebuild soil, and plant trees and vegetables. And they aren’t afraid to get arrested when it’s time to take a stand.

Rebuilding our economy will mean more people will have meaningful work. A more frugal society means less waste, less time devoted to “stuff,” and more time for things that make for genuine happiness (see Fight Climate Change: Live the Good Life). And we can create well-being that isn’t reliant on someone else sacrificing their own.

When we learn to live within our ecological means, we won’t need to fight wars over resources like oil or water. Men and women in uniform can be redeployed to the critical tasks of restoring damaged ecosystems, coping with the inevitable natural and climate-induced disasters, and revamping infrastructure so it can withstand the coming storms.

There Is Still Time

We can still avert the extreme droughts, floods, storms, and displacements that could result if climate change reaches critical tipping points. It’s still possible to save ourselves and generations to come from a climate so unstable that it can no longer support civilization as we know it. But we can’t leave it to our leaders to fix it; the possibility only exists if we rise up and act now.